This research program will investigate the functional properties of the limited population of monoamine-containing neurons within the leech nervous system. Nine of these ganglionic neurons contain serotonin and two contain catecholamine. These cells can be vital-stained with neutral red dye and are accessible for anatomical, biochemical, functional, and developmental studies. Regional variations in anatomy will be studied with the intracellular dyes horseradish peroxidase and Lucifer Yellow. Microradioenzymatic techniques will be employed to measure endogenous amines. The physiology and pharmacology of the synaptic and modulatory effects of amine cells upon muscular contraction, reflexive shortening, visceral motility and swimming behavior will be investigated with microelectrode recording, stimulating and iontophoretic techniques. The development of the amine cells will be studied with histochemical techniques (Falck-Hillarp) and with microelectrode studies of their structure and function. This program is intended to acquire fundamental data upon the structure, function and chemistry of the amine-containing cells as well as to describe the stages through which these biochemically-related cells develop.